The present invention relates to a method for measuring a pressure and recording a pressure distribution in a contact surface or a pressing site, and a pressure measuring film.
There has heretofore been a pressure measuring film for measuring a pressure (contact pressure) applied between contact surfaces. For example, xe2x80x9cPrescalexe2x80x9d (tradename) is presented by Fuji Photo Film Co., Ltd. This is obtained by forming a microcapsulated color former layer on the top surface of a support (film), and superposing a color developer layer thereon. By application of pressure, the microcapsules are destroyed to release the color former from the ruptured microcapsules. The released color former is adsorbed to the developer and a color is developed by chemical reaction.
In general, the pressure measuring film has a predetermined measurable pressure range. The diameter of the microcapsule is in a range of several microns to several tens of microns, and the microcapsule is easily destroyed as the diameter increases. Accordingly, the measurable pressure range can be set by changing the size of the microcapsule for use. In the conventional film, the measurable minimum pressure is 0.2 MPa (1 MPa is nearly equal to 10.2 kgf/cm2), and a pressure lower than the predetermined minimum pressure could not be measured.
As described above, in the conventional pressure measuring film, there is a problem that the measurable pressure ranges to 0.2 MPa at minimum and a lower pressure cannot be measured.
For example, in the case a contact pressure between a sheet conveying roller and a sheet is measured in a copying machine or a facsimile machine, if the contact pressure can be measured by bringing the pressure measuring film into contact with the conveying roller and conveying the film, the measurement can easily and conveniently be performed. However, such measuring operation cannot be realized because the contact pressure of the conveying roller is usually 0.2 MPa or less (usually in a range of 100 gf/cm2 to 2 kgf/cm2). Moreover, an extremely low pressure is sometimes set including the laminating pressure applied between front and rear glass substrates of a liquid crystal panel, the polishing pressure applied to a silicon wafer for use in a semiconductor manufacture process, and the like. The conventional pressure measuring film cannot be used for measuring such a extremely low pressure.
The conventional pressure measuring film has another problem that the contact pressure cannot be measured in an area having a size smaller than the size of the microcapsule. The measurable minimum pressure level can be decreased by increasing the size of the microcapsule. However, when the size of the microcapsules is enlarged, the minimum area where the applied pressure is to be detected is also enlarged. This results in less resolution of the pressure distribution. For example, in the field of manufacture of the semiconductor, there is need to measure the contact pressure of a bonding wire to an electrode. However, the microcapsule has a diameter of several tens of microns (1 micron=10xe2x88x926 m), while the bonding wire has a diameter of about one micron. Therefore, the conventional pressure measuring film cannot be used.
In order to lower the measurable pressure range and attain the high sensitivity, a rubber mat on which a large number of pyramid-shaped protrusions are formed is used so that the top of the pyramid abuts on the side of the pressure measuring film. The pressure applied to a pyramid bottom side converges to the tip top, and a force per unit area, that is, the pressure transmitted to the tip top can be increased. Accordingly, the pressure applied to the pressure measuring film through the tip top reaches to and is placed in the measurement range of the pressure measuring film. In this case, however, the minimum contact area to be measured is enlarged, and the pressure measuring film cannot measure the contact pressure of the bonding wire or the like. Moreover, since the conventional pressure measuring film is much influenced by a temperature and a humidity during use, the use condition needs to be strictly managed, which is inconvenient.
The present invention has been accomplished in consideration of the aforementioned circumstances, and a first object thereof is to provide a pressure measurement method in which an extremely low pressure applied to an extremely small contact area can be measured, and the influence of use conditions (temperature, humidity) is not easily exerted. A second object of the present invention is to provide a pressure measuring film for direct use in carrying out this method.
To attain the first object, according to the present invention, there is provided a method for measuring pressure comprising the steps of:
providing a pressure measuring film in which a toner layer with a definite thickness is held between an adhesive layer formed on a first support and an inactive adhesive layer formed on a second support;
subjecting said inactive adhesive layer to activation treatment, so that said in active adhesive layer become having an adhesive property;
applying the pressure to said pressure measuring film by contacting said pressure measuring film with a portion of an object where the pressure is to be measured;
stripping said first support from the pressure measuring film; and
examining the amount of a toner remaining on said second support to determine the applied pressure.
The inactive adhesive layer can be formed by an adhesive which is activated by a heating treatment or an adhesive which is activated by ultraviolet rays. For example, a thermoplastic resin-based adhesive will repeatedly soften when heated and harden when cooled at normal temperatures. Such thermoplastic adhesive is applied to the second support to harden, then laminated onto the toner layer. The thermoplastic adhesive layer is heated immediately before or during pressure measurement. In other words, the thermoplastic adhesive is reactivated by heating to recover its adhesive property. Moreover, the inactive adhesive layer may be formed lf a photo-plastic resin-based adhesive which can be activated by ultraviolet rays to soften so that the adhesive characteristics is revealed. In this case, it is preferably to use a transparent or translucent film as the second support to which the inactive adhesive is coated. The photo-plastic adhesive is activated by a radiation ray such as UV ray through the transparent support.
Additionally, xe2x80x9cactivationxe2x80x9d herein refers to a treatment for generating or recovering an adhesive force in the inactive adhesive, which has no adhesive properties in an atmosphere of ordinary air, by a special treatment (heating, ultraviolet irradiation or the like). A carbon toner is suitable as the toner for use in the toner layer. The carbon toner for use in a copying machine, a facsimile machine or the like is preferable because particle size of carton toner is extremely small. The toner is uniformly dispersed in a solvent and the resultant mixture is applied or coated on the adhesive layer. In the course of drying the layer of the dispersion mixture, toner particles are bonded to one another with a weak force to form a layered structure of toners on the adhesive layer.
The magnitude of the measurement pressure can be determined based on the density of the image recorded by the toner remaining on the second support. More specifically, in a place where high contact pressure is applied, there is remained much toner which is attached and fixed to the second support by the activated adhesive, so that the density of the toner image increases. Conversely, in a place where the contact pressure is low, the toner density on the second support decreases. The toner density may visually be judged, or measured by reading the toner image of the second support with a scanner. When the toner image is read by an image sensor such as CCD, the density can be determined from the output voltage of each pixel of the image sensor.
The toner layer may be formed, for example, only of a black toner. Alternatively, a plurality of different color toner layers may be formed as multiple layers. When the low pressure is applied, only the toner in the bottom toner layer adjoining to the activated adhesive is adhered to the activated adhesive and transferred to the second support, but other toners in the upper toner layers are not transferred to the second support. Namely, the color formed of different toners attached to the second support changes by the magnitude of the pressure, the magnitude of the applied pressure can be determined by reading the densities or hues of the color image by a color scanner or the like. Moreover, the color change can be detected by naked eyes easily. This is convenient for visually estimating the magnitude of the applied pressure.
To attain the second object, according to the present invention, there is provided a pressure measuring film comprising: first and second supports; an adhesive layer formed on said first support; an inactive adhesive layer formed on said second support; and a toner layer with a definite thickness held between said adhesive layer and said inactive adhesive layer.
The first and second supports is preferably polyethylene terephthalate (PET) resin films, respectively. The toner layer may be of a single color, or may be formed by laminating different color toners into a plurality of layers. Preferably, a toner fixing agent for fixing the toner is added to the toner layer so as to prevent the toner remaining on the second support flaking or flying in air. The addition of the toner fixing agent ensures an easy handling at the time when the image density of the second support is measured. Examples of such toner fixing agents includes a liquid adhesive of which a solvent evaporates in air, and a liquid adhesive which reacts with oxygen in air to generate an adhesive force.